Electric incandescent projection lamp having an improved dual-filament mount assembly,and method of making such assemblies



Sept. 22, 1970 A. R. DE CARO 3,530,326

ELECTRIC INCANDESCENT PROJECTION LAMP HAVING AN IMPROVED DUAL-FILAMENT MOUNT ASSEMBLY, AND METHOD OF MAKING SUCH ASSEMBLIES Filed Sept. 25, 1968 FIG.|.

WITNESSES 3Q INVENTOR Ar istide R. De Caro US. Cl. 313-115 Claims ABSTRACT OF THE DISCLOSURE The coiled-coil main and ballast filaments of an incandescent projection lamp are wound from refractory wire, such as tungsten, of the same diameter and are mounted as-wound on the reflector-stem assembly. The filaments are connected in series and their electrical characteristics and lighted lengths are controlled by correlating the pitch of the primary and secondary turns, the primary and secondary coil diameters and the spacing between the conductive supports to which they are attached. In a preferred embodiment, the main filament is fastened to its support wires by spot welding the coil legs to the wires and the lighted length of the main filament is controlled by molybdenum inserts which are placed within the coil legs and short-circuit the overlying segments of the legs that are located inwardly of the spot welded junctures.

BACKGROUND OF THE INVENTION This invention relates to electric lamps and has particular reference to an electric incandescent projection lamp having a main filament and a ballast filament that are connected in series, and to an improved method for manufacturing such filaments and mounting them on the stem assembly that is subsequently sealed into the lamp envelope.

Incandescent projection lamps having a main filament and a ballast filament that are positioned in predetermined relationship with an elliptical reflector inside a tubular envelope are well known in the art. A lamp of this type having a main filament of coiled-coil configuration and a ballast filament which is also of coiled-coil configuration but wound from smaller diameter wire and with a more open pitch compared to the main filament so as to have a lower thermal inertia and lower operating temperature is disclosed in US. Pat. Nos. 3,222,567 and 3,330,984. A dual-filament projection lamp of this general type having an improved reflector component and disclosing an alternative embodiment wherein the ballast filament is mounted behind the reflector is illustrated and described in US. Pat. No. 3,325,667.

While the aforementioned prior art lamps were satisfactory in that they improved the light output and strength of the lamp by reducing the size of the main filament and concentrating it at the focal point of the reflector, they were expensive and diflicult to manufacture since they required filaments wound from two different wire weights or sizes and required the services of a highly skilled operator to stretch the ballast filament to the required length and then adjust the support wires on which the filaments were mounted to obtain the proper optical alignment of the reflector and the main filament. Such coil stretching and adjustment of the mounted filaments frequently distorted them and produced undesirable changes and variations in the spacing between turns and other critical parameters which impaired the light output and light distribution and caused variations in the life of the finished lamps.

nited States Patent O Patented Sept. 22, I970 ice SUMMARY OF THE INVENTION It is accordingly the general object of the present invention to provide a dual-filament incandescent projection lamp that has a lower manufacturing cost compared to the prior art lamps and which has an improved light output, light distribution pattern and life.

A more specific object is the projection of an improved filament mount assembly for such a dual-filament projection lamp which can be rapidly manufactured without the complex optical mounting devices used heretofore and without distorting or impairing the quality of the filaments in any way.

Still another object is the provision of a method of manufacturing the dual filaments for such projection lamps and accurately controlling their electrical characteristics and location relative to the reflector during the filament mounting operation so that no adjustments of the mounted filaments are required.

The aforesaid objects and other advantages are achieved in accordance with the present invention by winding the main and ballast filaments from refractory metal Wire that has the same diameter, and by varying the turns-per-inch (t.p.i.) and diameters of the primary and secondary windings in conjunction with the lighted lengths of the respective filaments so that the latter can be mounted in the configurations in which they were Wound. The spacings between the support wires to which the filaments are attached are preset so that no adjustments of the filament-support assembly are required to properly locate the main filament with respect to the reflector or to obtain the t.p.i. and lighted lengths necessary to properly balance the electrical and thermal characteristics of both of the mounted filaments.

In a preferred embodiment, the lighted length of the main filament is controlled by placing refractory metal inserts into each of the coiled legs to short out preselected portions of the legs. Thus, the complicated and critical prior art practice of controlling this parameter by adjusting the spacing of the support wires after the main filament is mounted is eliminated. Utilization of the concepts of the present invention has permitted the lighted length of the main filament to be reduced to approximately /3 that of the ballast filament, thus increasing the strength of the main filament and increasing the amount of light concentrated at the film gate by the internal reflector.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIG. 1 is an enlarged perspective view of a dualfilament projection lamp embodying the invention;

FIG. 2 is a front elevational view of the filament mount assembly employed in the lamp shown in FIG. 1; and,

FIG. 3 is an enlarged elevational view of the main coiled-coil filament with an insert positioned in one of its legs and an insert partly placed in the other leg.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown an incandescent projection lamp 10 which embodies the invention and consists of a tubular glass envelope 12 that is hermetically sealed by a glass wafer-like stem 14 through which four rigid metal pins 15, 16, 17 and 18 are sealed. A concave metal reflector 20, preferably one of elliptical configuration, is supported in upstanding position within the envelope 12 by a pair of support wires 21 and 22 that are spot welded to the tabs on the lower edge of the reflector and to the inner ends of the pins 15 and 18, respectively. A third and longer reflector-support wire 23 is spot welded to the inner end of the pin 16 and extends upwardly behind the reflector 20' to the apex thereof where it is spot welded to one end of a main support wire 24 which, together with a second main support wire 25, is anchored in an insulator 26 that is secured in a suitable opening provided in the reflector.

A main filament 28 of coiled-coil configuration is fastened to the free ends of the main support wires 24, 25 in a position such that the coil barrel defined by the secondary turns 30 is located at the focal point of the reflector 20. A second coiled-coil filament 34 is held in upstanding position at the lower rim of the reflector 28 by an auxiliary support wire 38 that is attached to and depends downwardly from the main support wire 25 and by a second auxiliary support wire 40 which is fastened to the metal pin 17 and depends laterally therefrom. The ballast filament 34 is thus located remote from the focal point of the reflector 20 and from its optical axis. The ballast filament 34 is connected in series with the main filament 28 by virtue of the fact that one end of each of the filaments are connected to each other through the main support wire 25 and attached auxiliary support wire 38 and the opposite ends of the filaments are connected by the main support wire 24, reflector support wire 23 and auxiliary support wire 40 to pins 16 and 1.7, respectively, which serve as the lead-in conductors and the terminals for the lamp.

The auxiliary support wire 40 is provided with an intermediate fuse wire component 41 in accordance with standard lamp-making practice.

The sealed end of the envelope 12 is fitted with a metal base 44 that encloses the neck of the envelope and is provided with a keyed post 46 which insures that the lamp is properly oriented in its socket. The base 44 has suitably spaced openings in its bottom wall which snugly receive circular bosses molded in the outer surface of the stem 14 around each of the metal pins so that the latter are electrically insulated from one another. The wafer stem 14, reflector 20, main and ballast filaments 28 and 34, together with the interconnected support and lead wires form a unitary mount assembly 43, shown in FIG. 2. Evacuation of the sealedin lamp is achieved by means of a glass tubulation 19 sealed to the stem 14.

The essence of the present invention resides in the construction of the main filament 28 and ballast filament 34 and the manner in which they are attached to the mount assembly 43 and these features will now be described.

As will be noted in FIG. 3, the main filament 28 has a coil barrel that consists of a plurality of secondary turns 30 and is terminated at each end by a straight axially-extending coiled leg section 32 into which an insert 33 is placed. The inserts 33 are of predetermined length and of such diameter that they effect a force fit with the coiled legs and are preferably forced into the respective legs until they are flush with the ends thereof. Hence, predetermined end segments of each of the coiled legs 32 are shorted out by the inserts 33 so that the lighted length (dimension x in FIGS. 2 and 3) of the main filament 28 is equivalent to that portion of the coil that extends between the innermost ends of the leg inserts 33 and includes the coil barrel and a small part of each of the respective legs.

As shown in FIGS. 1 and 2, the insert-containing legs 32 of the main filament are spot welded to the main support wires 24, 25 so that the coil barrel is located at the focal point of the elliptical reflector 20. The main support wires 24, 25 lie in a plane that contains the focal point of the reflector 20 and its optical axis. The positioning of the main filament 28 with respect to the focal point of the reflector 20 is thus effected by properly positioning the filament on the wires as by means of a suitable jig, and then spot welding the members together. The spacing between the main support wires 24, 25 and the lengths of the coil legs 32 and inserts 33 are such that the overall length of the filament 28 is larger than the lead spacing, thus permitting the necessary lateral adjustments between the supports and filament to be made prior to the spot welding operation. The main filament 28 is thus mounted on its support wires in the condition in which it was formed and no adjustment of the position of the main support wires 24 and 25 is required after filament mounting which would tend to distort or otherwise change the electric or physical characteristics of the main filament.

The same construction and mode of filament mounting is employed in the case of the ballast filament 34, except that this filament is secured to its support members 38, 40 by means of clamps and leg inserts are not employed. As shown in FIGS. 1 and 2, the auxiliary support wire 38 has a clamp 39 formed on its free end and the other auxiliary support 40 has a similar clamp 42 formed at its free end. Prior to the filament mounting operation, the clamp portions of the auxiliary support wires 38 and 40* are spaced a predetermined distance apart and the lighted length of the ballast filament 34 (which is equivalent to the portion of the filament located between the clamps 39 and 42) is such that the thermal and electrical characteristics of the ballast filament 34 are properly correlated with those of the main filament 28. These characteristics, are of course, also governed by the wire weight, pitch, etc. and these parameters are so selected that the main filament 28 operates at a higher temperature than the ballast filament 34 and the latter heats up more rapidly and reaches its operating temperature before the main filament.

Mounting of the ballast filament 34 is achieved by first spacing the clamp portions of the auxiliary support wires 38 and 40 a predetermined distance apart, positioning the ballast filament so that its coil legs 36 lie within the clamps 39, 42 and a predetermined number of primary turns extend beyond each of the clamps, and then closing the clamps to lock the filament in place on the support wires. Both the main filament 28 and the auxiliary filament 34 are thus secured to their respective support wires without any stretching or altering of the primary or secondary turns of the respective filaments either before or after the filament mounting operation. The filaments are thus mounted in their as wound condition and their physical and electrical characteristics are thus very accurately controlled and correlated.

Following is a specific example of one embodiment of the invention. A T12 incandescent projection lamp having a nominal rating of 150 watts and 115420 volts was provided with a main filament 28 formed of 3.07 mil tungsten wire that was wound on a 13 mil mandrel into a primary coil having an outside diameter of approximately 19 mils, which primary coil was then wound on a retractable type coil-winding machine around a secondary mandrel which had a diameter of 42 mils to form a coiled-coil filament of the type shown in FIGS. 1 to 3. The primary turns of the main filament were wound at 204 turns per inch, the secondary turns forming the coil barrel were wound at 37.3 turns per inch, the coil diameter of the barrel was approximately mils, the overall length of the coil was 21 millimeters and the coil legs at each end each had a length of 8 millimeters. The inserts were made of molybdenum, were each 8 millimeters long and had an outside diameter of 12 mils. The lighted length of the main filament (dimension x in FIGS. 2 and 3) was accordingly approximately 5 millimeters.

The ballast filament 34 was also wound from tungsten wire having a diameter of 3.07 mils but the primary winding was wound at 172 turns per inch on a 12 mil mandrel and the diameter of the primary coil was approximately 18 mils. The primary coil was wound around a retractable mandrel 25.6 mils in diamenter at 21 turns per inch and the outside diameter of the resulting coil barrel was approximately 61 mils. The overall length of the ballast filament was 23.5 millimeters and it also had a leg 8 millimeters long at each end.

The spacing between the main support wires 24, 25 was 15 millimeters but, as was pointed out above, the use of the inserts in each of the coiled legs reduced the actual lighted length of the main filament to approximately millimeters. The spacing between the clamps 39, 42 at the ends of the auxiliary support wires 38, 40 was also 15 millimeters so that the lighted length of the ballast filament was, therefore, also 15 millimeters Tests on lamps made with the foregoing filaments have shown that the main filament 28 operated at a higher temperature (298 C.) than the ballast filament 34 (285 C.) and that the latter, due to the smaller number of primary and secondary turns-per-inch, reached its operating temperature more rapidly than the main filament and had a longer operating life. The use of spot welded junctures and molybdenum leg inserts not only accurately controlled the lighted length of the main filament 28 but reduced its unsupported lighted length so that it was only a third as long as that of the ballast filament thereby providing a much shorter main filament than those heretofore employed in the prior art and providing a much stronger filament mount. It has also been found that about 55% of the power input is consumed by the main filament and about 45% of the input is consumed by the ballast filament. Since the spacings between the paired main and auxiliary support wires are fixed and the main and ballast filaments are mounted in their aswound" condition, the filaments are not distorted in any Way after they are mounted and the spacing between turns, etc. remain unchanged. Lamps manufactured in accordance with the present invention accordingly have a higher light output, an improved projected light pattern and an improved and more uniform lamp life.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that an inexpensive method of manufacturing the main and ballast filaments for a projection lamp by using filamentary wire of the same size and then fastening them to the support wires of the mount assembly have been provided.

While one embodiment has been illustrated and described, it will be appreciated that various modifications in the construction of the filaments and manner in which they are wound and mounted can be made without departing form the spirit and scope of the invention.

I claim as my invention:

1. In an electric incandescent projection lamp comprising an hermetically sealed envelope that contains a concave reflector and a pair of lead-in conductors which extend through the wall of said envelope, the improvement comprising:

a main filament and a ballast filament of coiled-coil linear configuration wound from refractory metal wire of the same diameter, and

means (a) supporting said main filament at the focal point of said reflector and said ballast filament at a location remote from said focal point and the optical axis of said reflector and (b) connecting said main and ballest filaments to said lead-in conductors in series relationship with one another,

the primary and secondary turns-per-inch and the primary and secondary coil diameters of said main and ballast filaments being so correlated that said main filament operates at a higher temperature than said ballast filament and has a lighted length that is less than /2 that of said ballast filament.

2. The lamp set forth in claim 1 wherein;

said main and ballast filaments are terminated at each end by a coiled leg section consisting of a plurality of spaced primary turns,

said supporting means comprises a pair of main support wires and a pair of auxiliary support wires that are fastened to the coiled leg sections of the respective filaments, and

one of said main support wires is electrically connected to a preselected one of said pair of auxiliary support wires.

3. The lamp set forth in claim 2 wherein;

said reflector is composed of metal and is of ellipsoidal configuration,

the main support wires are fastened to the coiled leg sections of said main filament and are anchored in an insulator carried by said metal reflector,

one of said main support wires is connected to one of said pair of lead-in conductors and the other main support wire is spaced from both of said lead-in conductors, and one of said auxiliary support wires is joined to and depends from the main support wire that is spaced from said lead-in conductors and the other auxiliary support wire is joined to and depends from the leadin conductor that is spaced from said main support Wires.

'4. The lamp set forth in claim 2 wherein;

the spacing between said main support wires is substantially equal to the spacing between said auxiliary support wires,

said main and ballast filaments each have an overall length that exceeds the aforesaid spacing between the respective pairs of support wires, the pair of auxiliary support wires are clamped around the coiled leg sections of the ballast filament, and

the coiled leg sections of said main filament contain inserts of refractory metal and are spot welded to said main support wires.

5. The lamp set forth in claim 4 wherein said refractory metal inserts short-circuit predetermined portions of the coiled leg sections of the main filament so that the portion of said main filament that incandesces when the lamp is energized and thus constitutes the lighted length of the main filament is shorter than the length of the main filament that is disposed between said main support Wires.

6. The lamp set forth in claim 5 wherein;

said main and ballast filaments are wound from tungsten wire approximately 3 mils in diameter and the lamp is designed for operation at 115-120 volts,

the spacing between the paired main and auxiliary support wires is approximately 15 millimeters,

the main filament has an overall length of approximately 21 millimeters, a lighted length of approximately 5 millimeters, a coil barrel which has an outside diameter of approximately mils and a length of approximately 4 millimeters and consists of 5 secondary t-urns wound at approximately 37 turns per inch, and a primary coil that is approximately 19 mils in diameter and has 204 turns per inch, and

said ballast filament has an overall length of approximately 23 millimeters, a lighted length of approximately 15 millimeters, a coil barrel approximately 7 millimeters long and 61 mils in diameter that is terminated at each end by a leg section approximately 8 millimeters in length and includes 5 secondary turns wound at 21 turns per inch, and a primary coil that is approximately 18 mils in diameter and has 172 primary turns per inch.

7. The lamp set forth in claim 6 wherein:

said inserts are composed of molybdenum and shortcircuit approximately 8 millimeters of each of the coiled leg sections of the main filament so that the lighted length of the main filament is approximately 5 millimeters.

8. In the manufacture of a filament mount assembly for an electric incandescent projection lamp, which assembly includes a concave reflector, a pair of main support wires and a pair of auxiliary support wires that are interconnected and fastened to rigid lead-in conductors that are sealed through a vitreous stem with which they form an integral subassembly, said main support wires being so connected to said auxiliary support wires and said lead-in conductors that a main filament attached to said main support wires will be in series with said lead-in conductors and with a ballast filament that is attached to said auxiliary support wires, the method of fabricating said main and said ballast filaments and then mounting them on said main and auxiliary support wires in predetermined relation with each other and said reflector and concurrently controlling their electrical and physical parameters, which method comprises;

winding refractory metal wire of the same diameter into a coiled-coil main filament and a separate coiledcoil ballast filament having (a) predetermined overall lengths, (b) coiled leg sections at each end that are of predetermined length and diameter and consist of primary turns wound at a predetermined pitch, and (c) coil barrels of predetermined length and diameter consisting of a predetermined number of secondary turns wound at a predetermined pitch,

orienting said auxiliary support wires so that the free ends thereof are spaced a predetermined distance apart and are located remote from the focal point of said reflector and its optical axis,

orienting said main support wires so that the free ends thereof are spaced a predetermined distance apart and lie in a plane which contains the focal point and optical axis of said reflector,

=placing said ballast filament across the ends of said auxiliary support wires and orienting it so that predetermined portions of its coiled leg sections contact said auxiilary support wires,

placing said main filament across the ends of said main support wires so that predetermined portions of its coiled leg sections contact the main support wires and the barrel of said main filament is disposed at the focal point of the reflector, and then fastening said ballast and main filaments to their respective support wires while the components are maintained in the aforesaid spatial relationship so that said filaments are secured to the mount assembly in substantially the same configuration in which they were wound.

9. The method of claim 8 wherein;

clamps are formed on the ends of said auxiliary sup port wires prior to the attachment of the ballast fila ment,

a force fitting insert of refractory metal is placed into 8 each of the coiled leg sections of said main filament prior to the attachment thereof to said main support wires,

said inserts are positioned so that predetermined portions of said leg sections are short-circuited and said inserts thus define the lighted-length dimension of said main filament,

the auxiliary support wires are oriented so that the clamp portions thereof are spaced a predetermined distance apart,

the said predetermined portions of the leg sections of said ballast filament are disposed in the clamp portions of said auxiliary support wires,

the said predetermined portions of the leg sections of said main filament which contact said main support wires contain said inserts, and

said main and ballast filaments are fastened to their respective support wires by closing the clamp portions of said auxiliary support wires and spot welding the coiled leg portions of the main filament and inserts disposed therein to the contacting portions of the main support wires.

10. The method of claim 9 wherein said inserts are of predetermined length and are placed in the respective coiled leg sections of said main filament so that the outer ends of the inserts are substantially flush with the outer ends of the associated leg sections.

References Cited UNITED STATES PATENTS 3,325,667 6/1967 ONeill et al 3l3113 3,330,984 7/1967 Smith 3l3115 3,348,094 10/1967 Smith 3l3113 X 3,325,679 6/1967 Wiley 315-71 JAMES W. LAWRENCE, Primary Examiner D. OREILLY, Assistant Examiner US. Cl. X.R. 313273, 316 

